Ground States of Two-Dimensional Polyampholytes

TL;DR

This study investigates the ground state properties of two-dimensional polyampholytes with random charge sequences, revealing how excess charge influences their compactness and stretching behavior on a lattice.

Contribution

It provides the first exact enumeration analysis of 2D polyampholyte ground states, detailing effects of charge and sequence on their structural properties.

Findings

Neutral ground states are compact and energy is extensive.

Small excess charge causes ground state expansion.

In annealed ensemble, ground states are fully stretched for any Q>0.

Abstract

We perform an exact enumeration study of polymers formed from a (quenched) random sequence of charged monomers $\pm q_0$, restricted to a 2-dimensional square lattice. Monomers interact via a logarithmic (Coulomb) interaction. We study the ground state properties of the polymers as a function of their excess charge $Q$ for all possible charge sequences up to a polymer length N=18. We find that the ground state of the neutral ensemble is compact and its energy extensive and self-averaging. The addition of small excess charge causes an expansion of the ground state with the monomer density depending only on $Q$. In an annealed ensemble the ground state is fully stretched for any excess charge $Q>0$.